Apparatus for the late introduction of particulate alloy when casting a liquid metal

ABSTRACT

Apparatus for the late introduction of a particulate alloy when casting liquid metal, disposed between a casting ladle or an apparatus for the automatic feed of said metal and a series of moulds to be filled, characterised in that it comprises a jet of liquid metal of sufficient thickness, which is confined and in motion in a mixing chamber, for example a vortex, and a non-immersed introduction means (8) for the introduction of particles of alloy, imparting to said particles a speed and an energy sufficient for them to penetrate deeply into the interior of the liquid metal in the zone (4) of sufficient thickness, said zone being disposed in the vicinity of a casting orifice (5).

This is a divisional of application Ser. No. 08/075,485 filed on Jun.16, 1993 now abandoned.

FIELD OF THE INVENTION

The invention concerns an apparatus and a process for the lateintroduction of particulate alloy (powder or gain) when casting a liquidmetal (in general cast iron).

DESCRIPTION OF RELATED ART

The invention is intended in particular for the discontinuous casting ofshaped parts in series of medium and great length in moulds obtained byautomatic machines.

It is known that it is advantageous to effect the late introduction ofagents for the treatment of cast iron (nodulising and/or inoculatingagents) to obtain a quality which is as reproducible as possible of castparts of cast iron and a good yield on the part of the treatment agentsused, in particular when the agent contains magnesium which is volatileand difficult to dissolve in the liquid cast iron.

The late introduction operation can be carried out in a casting ladlejust prior to the casting operation, but that results in an inadequateyield and insufficient regularity in terms of quality of the cast parts.

It is also possible to use the "in mould" procedure which involvesproviding at the entrance of the casting mould a recess in which thetreatment agent will be disposed in such a way that it is regularlydissolved by the cast iron in a molten condition as it passes into themould. That procedure is effective but it is also long and difficult tocarry into effect, and in particular the configuration of the geometryof the cast iron feed passages has to be carefully designed in order toavoid the possible entrainment of endogenous or exogenous inclusionswithin the cast part.

That procedure is preferably reserved for long runs which make itpossible to amortize the cost of development of the mould.

The document FR 2 588 571 also discloses an apparatus in which thetreatment agent is introduced by means of a gas under low pressure intoa closed treatment chamber which is also under low pressure and in whichliquid metal to be treated and cast is disposed. Such a pressurisedarrangement permits good dissolution of the agents, in particular Mg,and the production of cast parts of high quality, but it raises problemsin terms of operation (fouling, blockage of the vents or risers,untimely accumulation of undissolved agent etc . . . ) when there is awish to carry out discontinuous casting operations in series.

A similar apparatus is known from the documents EP 30 220 or BE 639 410.The treatment agent is added by means of a carrier gas to the surface ofthe liquid cast iron which is set in motion in the form of a vortexwithin a chamber. In EP 30 220 it is preferable for said chamber to beclosed by a sealing cover in order to improve the efficiency of use ofthe agent when it is volatile (for example if it contains magnesium).This apparatus which is used for discontinuous casting operations inseries with a frequent interruption in the jet of metal between twocasting operations suffers from the same type of disadvantages asdiscussed above and requires the presence of a chamber which is sealedunder pressure to facilitate the introduction of the volatile agent andto improve its effectiveness and the quality of homogeneity of thecasting operations.

It is known also that, to introduce a treatment agent into liquid castiron, it is possible to use immersed lances in which the agent ispropelled by a carrier gas, but that makes it necessary always to have asubstantial minimum amount of liquid metal (residue) and in addition thecarrier gas is a considerable source of cooling and thereforesolidification of the liquid metal.

SUMMARY OF THE INVENTION

Confronted with those problems the applicants sought to provide anapparatus which is simple to use and easy to adapt in particular todiscontinuous casting of small runs of parts with the late introductionof treatment agents, in particular those comprising volatile elementssuch as Mg and/or which are little soluble in liquid metal.

The applicants also sought to provide a process which improves thelevels of efficiency of use of the treatment agent added and the degreeof constancy of the quality of the cast parts produced.

The invention is an apparatus for the late introduction of particulatealloys when casting liquid metal characterised in that it comprises ajet of liquid metal of sufficient thickness, which is confined and inmotion in a mixing chamber and an introduction means, which is notimmersed, for the introduction in said jet of particles of alloy,imparting to said particles a speed and an energy which are sufficientfor them to penetrate deeply into the interior of the liquid metal inthe zone of sufficient thickness, said zone being disposed in thevicinity of a casting orifice.

The apparatus according to the invention is generally placed between acasting ladle or furnace containing the liquid metal to be treated andcast and the mould or moulds which is or are to receive said metal.

The apparatus is particularly suited to the introduction of particulatealloy which is little soluble in the liquid metal and/or which containsa volatile element, in procedures for the discontinuous casting ofseries of parts, that is to say involving stopping the casting of theliquid metal between each cast part. Indeed, in the case of a highlyvolatile additive element such as magnesium, it is highly important thatthe speed of the particles and their depth of penetration is sufficientfor the highly volatile element to be liberated and to react only withinthe liquid metal in order to improve the quality of the treated metaland the efficiency of the addition.

The jet of liquid metal which circulates in the mixing chamber,preferably at a constant flow rate, must be of a sufficient thickness inline with the zone of injection of the particles so that said thicknessis greater than the depth of penetration of the particles (for exampleby at least 30%); it must be confined in such a way that the liquidmetal is not dispersed upon injection of the particles.

In fact, injection into a jet of liquid metal flowing in the open air isnot appropriate as the result obtained is generally inadequate mixingand dispersion of the jet of liquid metal as soon as the attempt is madefor example to increase the speed of injection of the particles by meansof a carrier gas, and that finally prevents introduction of theparticles into the liquid metal and filling of the mould for the part tobe cast.

Once treated, the jet of liquid metal is rapidly discharged from themixing chamber by way of a casting orifice which is disposed in thebottom, thus feeding the mould for the part to be cast.

It is advantageous for the jet of liquid metal of sufficient thicknessto be formed by a vortex which is produced by means of a runner for thefeed of liquid metal, under the effect of gravity, which openstangentially at the periphery of a rotationally symmetrical mixingchamber (being cylindrical or frustoconical) which is open upwardly, andin the vicinity of the lower part of said chamber, the bottom of whichis generally profiled in such a way as to facilitate the formation ofthe vortex. The bottom of the chamber comprises the casting orifice byway of which the treated liquid metal flows away.

The particulate alloy is introduced into the jet of liquid metal, ingeneral by means of a lance which is necessarily not immersed in theliquid metal. The lance is fed by a carrier gas at high speed, which ispreferably inert with respect to the cast metal and which carries theparticulate alloy, in such a way that said alloy issues from the lance,or any other introduction means, with a speed or an energy sufficient topenetrate, by violent projection, into the interior of the liquid metalin general by a depth of at least 1 cm and preferably about 2 cm.

It is noted that the depth of penetration of the particles is stillmarkedly greater than that of the carrier gas; that therefore avoids anyunacceptable scattering or cooling of the liquid metal.

The feed for the jet of liquid metal may be from a casting ladle oflarge dimensions by way of a funnel provided with a calibrated outletnozzle for regulating the flow of liquid metal or from a system for theautomatic supply of casting moulds.

The mixing chamber may be provided with an overflow orifice.

It is important for the jet of particles to be suitably oriented withrespect to the flow of the liquid metal, taking account of thecharacteristics of the flow of liquid metal: speed, geometry, physicalcharacteristics of the liquid metal, etc.

The projection lance can be connected directly to a container forparticulate alloy which is supplied by means of a carrier gas, the flowrate and the pressure of which are sufficient to impart to the alloy theenergy required for penetration into the liquid metal. The speed of thegrains is of the order of 10 m/sec.

However, it is preferable to use a lance equipped with its own ejectionsystem. In that case it is possible for it to be connected on the onehand to any particulate alloy container, which does not need to be putunder pressure, by way of a distributor means (for example of vibratingtype or of cell type or of guillotine type), and on the other hand to asource of carrier gas under pressure.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a non-limiting illustration of an apparatus according to theinvention using a vortex, in vertical section; it is provided with afunnel for the feed of liquid metal;

FIG. 2 is a plan view of the same apparatus but without the funnel; and

FIG. 3 shows a lance for projection by means of a carrier gas, fittedwith an ejection device for imparting speed to the particles of alloy,while permitting a substantial reduction in the speed of the gas at theoutlet.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, shown therein at reference 1 is the runner for thefeed of liquid metal (for example cast iron) towards the mixing chamber2. The runner opens at 3 tangentially to the periphery of the chamberand in the immediate vicinity of the vortex zone 4 which is prolonged bythe casting orifice 5. The chamber here is of frustoconical shape andhas a large opening 6 in its upper part and an overflow orifice 7.Reference 8 identifies the non-immersed lance 8 for the introduction athigh speed of the particulate alloy into the liquid metal of the vortex.A funnel has been installed at 9 to permit the runner 1 to be suppliedfrom a substantial casting ladle (not shown).

Referring to FIG. 2 where the funnel is not shown, reference 1identifies the runner which opens tangentially at 3 into the mixingchamber 2, reference 4 identifies the vortex zone, reference 5identifies the casting orifice, reference 6 identifies the upperopening, reference 7 identifies the overflow and reference 8 identifiesthe location of the non-immersed lance for introduction of theparticulate alloy.

Referring to FIG. 3 illustrating a lance for introducing particles,which is fitted with an ejection system imparting sufficient speed tothe particles to penetrate deeply into the liquid metal, reference 11identifies the particle supply tube which is connected to the reservoirfor particles, which may be a simple container and which does not needto be a reservoir under gas pressure; that communication is preferablymade by way of a particle distributing-metering means (not shown);reference 12 identifies a regulatable gas supply (generally fornitrogen) which is disposed at the level of the particle feed; reference13 identifies at a downstream location a constriction in the jet offluid of the venturi type, followed by a flaring enlargement 14 in thediameter of the outlet tube 15 of the non-immersed introduction lance.

The constriction 13 permits the flow of gas supplied by the tube 12 toimpart the necessary energy to the solid particles while the flaringenlargement 14 associated with the short length of the outlet tube 15makes it possible to slow down the gas while retaining the speed of theparticles.

The apparatus according to the invention thus makes it possible to carryout series of discontinuous casting operations with the lateintroduction of additives, on all types of moulds, without fouling orthe harmful accumulation of additive, being phenomena which are due tothe repeated stoppages of discontinuous casting, and without theexcessive danger of cooling due to the carrier gas.

It can be easily interposed between a casting ladle or an automatic feedcasting apparatus and the moulds without any precaution or particularadaptation, which means that it is an apparatus that is simple to use.It can be adapted to all types of foundry operations, in particularthose using automatic machines for the production of moulds in series.

This apparatus can be fitted with different regulating members (taps forthe feed of liquid metal of opening type and/or involving an adjustableflow rate and/or of controlled type, means for measuring the flow rateof liquid metal, powder or gas, level detection means, timing means forthe introduction of powder, etc . . . ), which permit the castingconditions to be optimised: for example casting a predetermined amountof liquid metal, introducing a corresponding metered amount of alloy atthe appropriate moment and for a desired period of time.

It is possible to make improvements:

in order to avoid excessively great dispersion of the jet of liquidmetal at the outlet of the casting hole of the apparatus, it isadvantageous for that hole to be of a polygonal, for example square,section;

maintaining the cleanliness of the casting hole may be effectedautomatically, between the casting operations, by passing into thecasting hole a tool of a section which is identical to that of thecasting hole, being operated for example by a jack, this cleaningoperation being effected at regular intervals and at a variablefrequency;

to simplify its cleaning operations which are carried out from time totime, the mixing chamber may be made up of two parts which are obtainedby cutting it in a vertical plane which preferably passes through thecasting hole, as represented by the line AA thereof in FIG. 2; those twoparts are generally assembled together by quick-fixing means.

Although it can be used for all types of liquid metal and all types ofadditives in powder form, it is particularly suited for the latetreatment for the nodulisation and/or inoculation of casting cast irons,for example by means of alloy Fe Si Mg containing from 40% to 75% of Siand from 3 to 30% of Mg.

It also makes it possible to improve quantitatively and qualitativelythe efficiency in regard to the introduction of alloys which are littlesoluble and/or which are volatile, such as those containing magnesium,that is to say by simultaneously improving the level of efficiency andits degree of regularity from one casting operation to another.

EXAMPLE

The results of levels of efficiency in regard to introducing magnesium,in terms of magnitude and stability, obtained with an apparatusaccording to the invention and in accordance with the prior art, will becompared.

Both cases involve using the same cast iron which is characterised bythe following chemical analysis:

C 3.7%

Si 2.7%

S 0.008%

Fe balance

and which served to cast ingots weighing 15 kg.

The treatment alloy used is of the following composition:

Mg 5.8%

Si 47%

Ca 0.54%

Aa 0.95%

Fe balance

and its granulometry is between 0.2 and 2 mm.

The amount introduced is 1.1% of the weight of cast iron.

TEST 1

This test involved using a casting apparatus illustrating the prior art.A vortex is formed by means of an arrangement corresponding to thatillustrated in FIGS. 1 and 2. In contrast the alloy is supplied by usinga cell-type metering device at atmospheric pressure, which is connectedto a distribution tube which by means of a carrier gas carries saidalloy onto the vortex of liquid cast iron.

In the ingots obtained, the level of efficiency (expressed by the ratiobetween the amount of magnesium observed in the cast iron and the amountof magnesium introduced) is found to range between 35 and 60%; inaddition, for levels of efficiency of lower than 45%, the graphite ofthe cast iron obtained is not totally nodular, which affects theproperties of the cast iron.

The poor levels of efficiency are due to irregularities in terms ofdissolution, which are manifested by fouling of the casting apparatus.

TEST 2

This Test involved using a casting apparatus according to the invention,corresponding to that illustrated in FIGS. 1 and 2, the alloy beingintroduced at depth into the vortex by means of a non-immersedprojection lance corresponding to that shown in FIG. 3, and imparting ahigh speed to the grains of alloy. The lance is fed by means of the samecell-type metering device as in Test 1.

The speed of the gases at the outlet of the lance is 20 m/s and thegrains penetrate to a depth of about 1 cm into the liquid cast iron ofthe vortex.

In the ingots obtained, the level of efficiency is found to rangebetween 50 and 65%, with a significant improvement in terms of value anddispersion; in all cases, the result obtained is a totally nodulargraphite structure.

The quality of the cast iron is suitably improved thereby.

What is claimed is:
 1. Method for the late introduction of particulatealloy into liquid metal during the casting of the metal, comprising thesteps of:providing a jet of liquid metal confined and in motion in amixing chamber having a casting orifice; mixing a particulate alloy witha carrier gas to speed and energy to said alloy, and subsequentlydecelerating said carrier gas without substantially decelerating saidparticulate alloy; introducing said particulate alloy into said chamberat a level above the jet of liquid metal, said particulate alloy havinga speed and energy imparted thereto sufficient to penetrate said jet ofliquid metal to a depth of at least 1 cm without penetration of saiddecelerated carrier gas to this depth; and casting said liquid metalmixed with said particulate alloy through said casting orifice. 2.Method according to claim 1, wherein vortex motion is imparted to saidjet of liquid metal in said mixing chamber.
 3. Method according to claim1, wherein the particulate alloy contains magnesium.
 4. Method accordingto claim 3, wherein the liquid metal is cast iron and the particulatealloy is based on Fe Si Mg.
 5. Method according to claim 1, wherein thespeed of the particulate alloy is about 10 m/s.